1. Field of the Invention
The present invention relates to a cleaning device, and more particularly to a cleaning device for use in removing toner particles on a member (such as image bearing members and intermediate transfer media) of an image forming apparatus such as copiers, facsimiles and printers. In addition, the present invention also relates to a process unit and an image forming apparatus including a cleaning device.
2. Discussion of the Background
In electrophotographic image forming apparatuses, toner particles remaining on a toner image bearing member such as image bearing members and intermediate transfer media even after a primary or secondary image transfer operation are removed therefrom with a cleaning device. Among various cleaning devices, blade cleaning devices are typically used because of having a simple structure and a good cleanability. A cleaning blade used for such blade cleaning devices is typically made of a polyurethane rubber and is set such that the tip edge of the blade is pressure-contacted with the peripheral surface of a toner image bearing member while the rear end portion of the blade is supported with a support to block and scrape off toner particles on a toner image bearing member. In general, a cleaning blade is attached to a toner image bearing member so as to be contacted with the entire surface of the toner image bearing member in the main image-scanning direction (i.e., the width direction of the toner image bearing member). Namely, the cleaning blade is contacted with an image forming region (i.e., the central portion of the member) and non-image forming regions (i.e., side end portions of the member). Such a cleaning device is disclosed in, for example, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2002-258701.
In order to well cleaning the surface of a toner image bearing member in the width direction thereof using a cleaning blade, the cleaning blade is preferably set so as to be contacted with the surface of the toner image bearing member at substantially the same pressure in the width direction. However, it is difficult to set a cleaning blade in such a manner. For example, parts constituting a cleaning blade have variations in size and therefore the cleaning blade assembled using such parts has also variations in size. When such a cleaning blade is used for a cylindrical toner image bearing member, a problem such that the cleaning blade is slantingly set (i.e., set so as not to be parallel to the axis of the toner image bearing member) occurs. In this case, the pressure of the cleaning blade at the side ends of the toner image bearing member is relatively low compared to that at the central portion of the toner image bearing member, thereby causing a problem in that toner particles on both side ends of the toner image bearing member are not well removed therefrom.
This defective cleaning due to positional variations of the set cleaning blade will be explained in detail using a drawing.
FIGS. 1A and 1B are views illustrating a cleaning blade which is set at a wrong position relative to a toner image bearing member due to positional variations of the blade. Referring to FIGS. 1A and 1B, an elastic blade 2 serving as a cleaning blade is set so as to be slanted at an angle of dθ relative to the axis of a photoreceptor 1 serving as an image bearing member. FIG. 1A is a schematic front view and FIG. 1B is a schematic side view. In FIG. 1A, the angle dθ is about 10 degree, but in reality the angle is much lower than 10 degree.
When positioning of the blade 2 is performed on the basis of a central portion 2c of the blade while the blade 2 is slanted at an angle of dθ, the tip of an end portion 2e of the blade 2 is apart from the surface of the photoreceptor 1 by a distance dL as illustrated in FIG. 1B. If the thus set blade 2 is pressure-contacted with the photoreceptor 1, the pressing strength of the end portion 2e at which the end portion 2e presses the surface of the photoreceptor 1 is lower than that of the central portion 2c because the degree of deformation of the tip of the end portion 2e pressed by the photoreceptor is smaller than that of the tip of the central portion 2c. Since the pressing strength of the end portion 2e is relatively low (i.e., the pressure of the end portion 2e is low), toner particles on the photoreceptor 1 tend to pass through the nip between the tip of the end portion 2e and the surface of the photoreceptor 1, resulting in occurrence of defective cleaning.
In this regard, the area of the contact portion of the end portion 2e, which is contacted with the surface of the photoreceptor 1, is relatively small compared to that of the central portion 2c. Therefore, the pressure per unit area of the end portion 2e is considered to be almost the same as that of the central portion 2c. However, the degree of deformation of the tip of the end portion 2e is smaller than that of the central portion 2c, the pressure caused by elasticity of the blade is lower at the end portion 2e than that at the central portion 2c. Therefore, the pressure per unit area of the end portion 2e is lower than that of the central portion 2c, resulting in occurrence of defective cleaning.
As a result of the present inventors' experiment in which a blade is intentionally set to be slanting, it was found that the cleanability of the end portions of the blade deteriorates. Thus, the theory mentioned above was confirmed.
In the above example illustrated in FIG. 1, cleaning of a cylindrical photoreceptor using a blade is explained. However, the material to be cleaned is not limited to such a cylindrical material, and the same is true for belt-form materials (such as endless belt photoreceptors and intermediate transfer media) if the materials have a curvature.
Because of these reasons, a need exists for a blade cleaning device which has good cleanability even when the blade is set to be slanted.